Monitoring of the course of diabetes in a patient may be accomplished by checking the glucose level in the blood. However, changes in this level are known to be especially rapid. Glucose assays can give only sporadic information about the patient's blood sugar level, and hence do not reflect the changes in the latter in the weeks preceding the analysis.
Quantitative determination of glycosylated hemoglobin Hb Al is known, moreover, to reflect a patient's average blood glucose concentration over a period of two months preceding the taking of a blood sample.
For this reason, assays of glycosylated (also termed glycated) hemoglobin are frequently used in medical analysis laboratories.
Hemoglobin consists of four peptide chains with a heme group. The main hemoglobin of normal adult subjects is hemoglobin A, consisting of two .alpha. chains and two .beta. chains.
Hemoglobin Alc is formed by nonenzymatic glycosylation of the .beta. chains of hemoglobin A by the binding of glucose to the free NH.sub.2 ends of the N-terminal valines of each .beta. chain.
Biochemical analysis shows that this Hb Alc fraction contains one mole of glucose per mole of hemoglobin.
The total glycosylated hemoglobin Al also comprises the fractions Ala, Alb, Ald and Ale. The first contains glucose 6-phosphate instead of unphosphorylated glucose; at the present time, little is yet known about the other three, but there does not appear to be any correlation between these fractions and the blood sugar balance.